Combined oscillator-detector circuit



Aug. 18, 1936. w. VAN B. ROBERTS COMBINED OSCILLATOR DETECTOR CIRCUIT Filed May 25, 1954 g INVENTOR J W on. a m on M.

ATTORNEY lllllllllllll |||||l||l I' l l atengteci i8, 193;

guirec STATES COMBINED OSCILLATOR-DETECTORV CIRCUIT Walter van B. Roberts, Princeton, N. J., assigner to Radio Corporation of America, a corporation of Delaware Application May 25, 1934, Serial No. '727,377

6 Claims.

energy which provides the local oscillations.V

Such a tickler coil, when utilized in a multi-range receiving set, necessitates the use of a doubleY switching connection between the local .oscillator coils, which coils are used for the different ranges, and the particular oscillator electrodes to which the coils are connected.

VIt may be stated that itis one of the main objects .of the present invention to provide a converter network; and particularly one of the electron coupled type, wherein simplified switching of the oscillator circuits for multi-range operation is secured by eliminating the use of a tickler c'oil, the oscillator electrode coupling being solely capacitative, and being provided by disposing the oscillator anode-and oscillator control grid in the converter tube in such a manner that the two electrodes are in similar phase with respect to their alternating voltages when connected for oscillation generation.

It is another important object of this invention to provide a converter of the electron coupled type, the converter being characterized by Vthe disposition of the oscillator anode electrode and the oscillator grid electrode in a region receiving an electron flow tending to be independent of the oscillator electrode potentials, the oscillator anode being vdisposed closer to the cathode than the oscillator grid, and the signal grid being disposed outside this region, the electrode construction creating a negative transconductance between the oscillator anode and the oscillator grid and thereby permitting oscillations to be produced by merely providing a capacity connection between the two oscillator electrodes to maintain them in similar phase with respect to their 'radio-frequency components of potential.

vAnother object-,of the invention is to provide a converter .of the electron coupled type wherein the oscillator electrodes are so geometrically related to each other and the remaining electrodes vof the tube that a negative transconductance is v created between .the Voscillator electrodes, the sigf nal grid being surrounded by a screen of. positive (Cl. Z50-20) potential disposed between the plate and the oscillator grid thereby permitting the use of automatic volume control bias potential on the signal grid to Vary the conversion gain of the converter tube without reducing the strength of the 5 locally produced oscillations.

Still other objects of the present invention are to improve combined oscillator-first detector circuits of present superheterodyne receivers, and more specifically to provide such converter cirl0 cuits which are not .only reliable in operation, but economically constructed and assembled in radio receivers.

The novel features which I believe to be characteristic of my invention are set forth in par- 15 ticularity in the appended claims. The invention itself, however, both as to its .organization and method of operation, will best be understood by reference to the following description taken in connection with the drawing, in which I have 20 indicated diagrammatically several circuit organizations whereby my invention may be carried into effect.

In the drawingz- Y Fig. 1 diagrammatically shows a superhetero- 25 dyne receiver embodying the invention,

Fig. 1A shows a fragmentary portion of. the system shown in Fig. 1, embodying a wave range switching device,

Fig. 2 shows a modified form of converter tube, 30

Fig. 3 shows still another modification of the invention.

Referring now to the accompanying drawing, wherein like reference characters in the differ# ent figures represent similar circuit elements,'35 there is shown in Fig.V 1 a superheterodyne receiver of conventional construction, except for the converter network. This receiver embodies the usual intermediate frequency amplifier preceded by a combined local oscillator-first de- 40 tector circuit, and followed by a second detector. The output of the second detector is impressed upon an audio amplifier network, and the latter may comprise one, or more, stages of audio amplication and/ or a reproducer of any well known type. The signal input'circuit of. the converter tube 2R`I comprises a tunable signal circuit including coil l and variable tuning condenser 2, the high alternating voltage side of the inputV circuit being connected to a signal collector, such as an antenna circuit. rThe low alternating voltage side of the input circuit is connected to ground through a source of negative grid biasing voltage N. The signal output circuit of the converter tube comprises the usualintermediate fre- Vbe taken as the reference The plate of the tubeY quency coupling transformer M having its pri,-

Ymary and secondary windings tuned to the operating intermediate frequency. Since these Vvarious networks of a superheterodyne receiver are is designated by the reference character P, and

' posed live cold electrode'sGi to G5 inclusive. t t tween the electrode G2 and the cathode there is this'rplate Vis connected to the high alternating voltage side of the primary circuit of transformer M. The plate P is connected to the positive terminal of a voltage source B, the latter not being y shown to preserve simplicity of disclosure. Between the cathode VC andthe plate P are dis- Be- Y disposedthe signalgrid G1, and the signal Vgrid is connected to the high alternating voltageV side of the tunable signal input circuit. t

The reference character G3 denotes the local oscillator anode electrode, while the reference character G4 denotes the local Aoscillator grid VV,which is disposed between the electrode G3 and thefpositiv'e screen electrode G5.Y It will be noted that eachfof the grids G1 and G4 is represented by'a zigzag line; the positive screen electrodes are denoted by short parallellines and the oscillator anode G3 Yis denoted by aline VVof small circles." These symbolic*reprepresentations are employed throughout the remainder of the drawing to' denoteV these various` electrodes. Y The screen electrodes G2 fand G5 are connected to.

sources of positive voltage S, while .the oscillator grid G4 is co'nnectedto a source of negative YVoltage through a leak resistor 3.V The oscillator anode G3 is connected to a source of positive :voltage O' through the tunable oscillator circuit which includes Vthe coiled and the variable tuning condenser 5. "'A' condenser 6 ofpreferably large capacity is connected between the oscillator grid G4 kand the oscillator anode G3. YThe dotted VlineV 'l denotes ar mechanical uni-control arrangement connected betweenthe'rotors of the tuning con-A VdensersV 2 and 3. It will beunderstoodrof course, th'atthe tunable signal circuit andthe tunable local oscillator circuit differ-from, each other at .j` Yall timesfby'the operating int'ermediate'fre- Yquency. Again, the-input circuit l, 2 need not beV coupled tothe antenna, butomay be preceded'by one, orjmore, stages 4of tunable radio frequency amplification.

` The tube ,'2R1 `is similar in principle to the 2Al, typetubefthe pentagrid converter, inthat theelectrode G2 is a screen electrode, on both sides of which control voltages act on the electron streamfiowing tothe plate P. However, the tube differs' from the 2A? type tubeV in that a local oscillator system is employed which is oftheV constant currenttype. The use of such an oscil-v.: lator involves advantageswhich will be pointed out below. Y Y

The radio frequency potentials of electrodes Y Gg'and vG4V are ofthe same phase due to the couplingcondenser 6, but the direct'currentpotentialsare notthe same. A constant current, neglecting signal input, emerges from the screen Y electrode ,(a, and dividesbetween thefeleictrode G3 onthe `one hand and the combination G5-P Y onthe other hand. When G4 is more'negative, the now ofY electrons to Gs-P is decreased, and

.hence the electrode G3 takes up the extra current Vdensers.

lost to the plate l5 and G5. Since this constitutes a negative transconductance between G4 and Ga, the local oscillatorV circuit is caused to oscillate by the feedback condenser 6. As far as the effect on the plate current goes, the resultant eiect of electrodes G3 and VG4 is the same as that of a single control grid between electrodes G2 and G5 supplied with local oscillator voltage. The electrode G5, if desired, may be omitted, Vor it may be connected within the tube to the Velectrode G2.

Its essential function is to provide'a high out'-V put impedance for the plate P, and it is pointed out that this may, also, be accomplished by leavingy a large spacing between e1ectrodes'G4 Vand P. The voltages N, Se, O and B may be derived from,V a single potentiometer connected across theV usual power supply system. Instead of operating the oscillator grid G4' from an external source of negative voltagethrough leak 3, it is Valso within the scope of the present inventionV to con-V nect the oscillator grid ,to a self bias resistor in thecathodelead. This is, also, true in connection with the biasvoltage N, since the usual grid Y biasing networkmay be disposed in the cathode lead to provide thenegative voltage for signal grid G1. The referenceL character 8 denotes Ythe usual connector cap provided on the,l converter tube.

tance between the oscillator anode "and grid Vis negative, acoupling condenser 6 is .sufficient to provide theY feedback foroscillation. It is'not necessary` toutilize a yfeedback coil toV provide the VVproperregenerative phase relationship,tasY in the case of circuits'known in the prior art of this type. Because of this present construction, only a single connection'may be. utilized betweenthe oscillator anode G3 andthe tunableroscillator cir- VIt will be observed'that since the transconduc-4 cuit. The value of this single connection advan- Y tage is in the case where the converter network 'is Vemployed in an all-wave set. 1 In Fig. 1A there is shown afragmentaryportion of a multi-range set using the converter network in Fig. 1, only the electrodesGa andG4 beingshown. The numeral 4. designates a tuning coil arranged to be connected inshunt with the coil 4, a switch 5 being utilizedto make the shunt connection. When the switch isopen, then variation of the tuning condenser 5 will result in tuning the local oscillator throughV the broadcast range, or more generally the longer wave length range, of local oscillation frequencies.V When the switch 5' is closed, thesmaller tuning coil 4 is connected in shunt with coil 4, and variation of l Y condenser 5v will then tune the local oscillator network through the shorter wave length range'of local oscillation frequencies.v It Willbe observed that tochange from Vthe long wave ranger to the.

Shortwave range it is only. necessary to manipulate the singleswitch 5. 'I'his is a distinct 'advan-V tage'over the prior4 art, wherein two connections would have to be,V changed, and this advantage is secured by virture ofthe construction ofthe tube 2R31,V Y t t The local oscillatorcircuit can readily berearrangedto` 'allow grounding Ythe tuning contween G3 and the sourceof positive potential inV For examplathe tuned circuit may be f ground v(in place of`fleak,3) s y place of the tuned circuit. 'In'genera'L the condi-L tions'necessary to produce oscillation "are merely quency potentials, to provide a tuned (anti-'res- Vto connect G3 and G4 together as to radio frebetween one of these electrodes and the cathode, and to maintain the direct potential of Gasomewhat negative, and the direct potential of G3 'positive. In actual practice, the total number of prongs to be used for tube ZRT may be reduced by utilizing the construction shown in Fig. 2, especially if high frequencies are to be generated.

It will be observed that in this construction the coupling condenser 6 of Fig. 1 is replaced by the inherent capacity 6', shown in dotted lines, between the oscillator anode G3 and the oscillator grid G4. The leak return 3 is disposed within the tube enevolope, and is connected to the cathode C. It will be observed that only seven prongs need be utilized in connection with the tube. Only a small capacity coupling is required because at very high frequencies it is sufficient, while at medium frequencies the high circuit impedances make a small coupling sufcient.

When it is desired to regulate the gain of the tube ZRT in dependence upon the received signal amplitude, thus providing automatic volume control, it is only necessary to re-arrange the electrodes of the tube in the manner shown in Fig. 3. In this case the signal grid G1 is disposed between the positive screen electrodes G2 and G5. The two screen electrodes may be connected together to a common source of positive voltage S. The oscillator anode Gg is disposed between the oscillator grid G4 and a positive cold electrode G6, the latter being constructed in a manner similar to the other two positive screen electrodes. 'Ihe electrode Gs is disposed adjacent the cathode C. The three screen electrodes Gs, G2 and G5 may be connected to the same voltage source S, unless Ge is located rather close to the cathode.

The normal negative bias on the signal grid G1 is secured by disposing the usual grid biasing network ZB in the grounded lead of cathode C, and in this modification the positive voltage is supplied to the oscillator anode G3 through a choke 2| which parallels the tunable oscillator circuit 4, 5. The low alternating voltage side of the tunable oscillator circuit is grounded.V A condenser 22 connects the oscillator anode side of coil 2| tothe high alternating voltage side ofthe tunable circuit 4, 5, and the plate P receives its positive voltage from the source B, as in the case of Fig. 1.

The AVC voltage is supplied to the signal grid G1 through any desired type of automatic volume 'control circuit, and in Fig. 3 the usual AVC rectifier is represented by a square, the negative side of the impedance (not shown) which develops the control voltage being connected by the AVC lead to the low alternating voltage side of the tunable signal circuit I, Z.- The AVC network is grounded in order to provide a path for the fixed negative bias impressed on the signal grid G1, and numerals 30 and 30 designate the pulsating current filter elements usually employed in the AVC network. It is to be clearly understood that the invention is not limited to the use of any specic type of AVC circuit, but that the legend AVC rectifier is intended to represent any well known form of rectifier circuit which is adapted to convert the received signal energy into a direct current voltage proportional to the amplitude of the received signal energy at all times.

In this way the negative bias of the signal grid G1 is increased when received signal amplitude increases, and is decreased when the signal am` plitude decreases. Thus, the gain of tube ZRT is a maximum when weak signals are received, and is a minimum when strong signals are received, this gain variation resulting in a compensation of fading effects and other undesired effects. Since those skilled in the art are well acquainted with the types of AVC systems which may be employed in the arrangement shown in Fig. 3, it is not believed necessary to make any further description of this element of the receiving system.

The arrangement shown in Fig. 3 permitsthe automatic volume control voltage to be applied to the signal grid G1 without reducing the strength of the local oscillations generated. This is so be cause the electron current to the oscillator electrodes is not reduced by placing a large negative bias on G1. Large bias on G1 merely prevents current from reaching Ythe plate, the loss of plate current being compensated by the increase of current to G2.

In each of the arrangements shown in this application the frequency changing function, or heterodyning function, is accomplished by electron coupling. It will be observed that, as in Fig. 1, the electron stream emanated from the cathode C to the plate P is modulated in accordance with the signal currents impressed upon signal grid G1. These modulated electron currents are further aifected by the oscillations generated in the local oscillator section of the tube. The resultant of these effects on the electron stream is applied to the plate P. The various frequencies produced in the circuit associated with the plate P are re-` jected with the exception of the intermediate frequency.

In the case of Fig. 3 the reverse action takes place; that is to say, the signal currents modulate the oscillation frequency-modulated electron currents flowing to the plate P.' It is toibe clearly understood that these aforementioned statements concerning the nature of the frequency changing action of tube ZRT are merely explanatory and theoretical in nature. Reference is made to the application of J. C. Smith, Serial No. 654,421, filed January 31, 1933 for a more detailed explanation of the frequency changing phenomenon which occurs in the ZAT or pentagrid converter tube.

While I have indicated and describedV several systems for carrying my invention into eifect, it

will be apparent to one skilled in the a'rt that my invention is by no means limited to the particular organizations shown and described, `vbut that many modifications may be made without departing from the scope of my invention, as set forth in the appended claims. Y

What I claim istv 1. In combination, an electron discharge tube comprising a tube envelope of the evacuated type, a cathode disposed within the tube envelope, a plate disposed within the tube envelope and spaced from said cathode, at least five cold electrodes disposed between said cathode and plate, one of said cold electrodes being adapted to function as Van oscillator anode, a second of said cold electrodes being adapted to function as an oscillator grid and being disposed between the oscillator anode and the said plate, means for positively charging two of said cold electrodes and surrounding the oscillator anode and oscillator grid with a positive potential surface, the other of said cold electrodes being adapted to function as a signalgrid and being disposed outside said positive surface,.means for impresing a modulated carrier frequency voltage on said signalY grid, a circuit tunable to a local oscillation frequency connected tosaid oscillator anode, and means including the inherent capacity between said oscillator anode and;V oscillatorV gridto? provide coupling between these last two named electrodes.

i 2; Inr combinatioman electron discharge Vtube comprising a tube envelope, of the evacuated type, a cathode disposed within the tube envelope, a

`plate disposed within Vthe tube envelope andfspaced from said cathode, at least iive'cold electrodesfdis- Y i posed between'said cathode and plateoneofy said cold electrodes being adaptedto function as an oscillator, anode, a second of. said cold electrodes being' adapted to function as ariQoscillator` grid and being disposed between` theoscillator anode and; the'said plate, two of said cold electrodes being positively charged and surroundingv the oscillator; anode and oscillator grid, means for applying said positive charge, the other of said cold electrodes Ybeing adapted to functionv as a signal grid, a leak resistor Vdisposed within said tube envelope` con-f nected @between thesaid oscillator grid and said cathode, a circuit tunable to the incoming signal frequency connected between said signalgrid and cathode, and a circuit tunable to a local oscilla. tion frequency coupled to said oscillator ianode,

and said oscillator gridhavinganegative'transconductance with respect to the oscillator anode.

3. In combination,an electronY discharge tube comprising a' tube envelope offthe'evacuated type, acathode disposed within the tubel envelope, a plate disposed within. the tube envelope and spaced yfrom said cathode, at leastliive'cold elecvtrodes disposed between said cathode andplate,

Yone of said cold electrodesV being adapted to function as an oscillator anode, a second of said cold 'electrodes being adapted to function as `an oscillator grid andbeingrdisposedbetween the oscillator anode and the said'plate, two of said cold Y electrodes being;V positivelyV charged n andY sur- Yvided betweenl rounding the oscillator anode and oscillatorgrid,

Y means for applying said positive charge to the 40 Y saidV tube having associatedwith it a Vtunable sig- Y said two electrodes, the other of said cold electrodes being Yadapted to function as asignal grid,

ne'cted to saidfplata'and-a signal input circuit`V connected between the signal grid and cathode, a

pair of oscillator electrodes disposed in the electron'stream between the cathode and plate, said oscillator` electrodes comprising' an` electrode adapted to functionras an oscillator anode, and

an electrode adapted;to;v function as anV oscillator grid, said oscillatoranode being disposed closer to the cathode than-theoscillator grid, a'constant; positive potential screen disposed between saidV cathode and oscillator anode `for; producingfa negative transconductan'ce between said oscilla Vtor electrodes, meansproviding purely capacity coupling betweenthe two oscillator electrodes, a `tunable localy oscillatorr networkconnected to Yat least onerof'said oscillator electrodes, saidtunable network consisting of a variable tuning condenser, a plurality Vof'coilshaving` diiferent inductances and means whereby one only Vortwo of said coils may be. connected inI shuntV with Vsaid condenser. Y

5.v An electron discharge tube comprising a tubeA envelope of the evacuatedftype,V a cathode disposed within the tubeenvelope, Ial-plate disposed within the tube envelope and spaced from saidrcathode,Y

at least i'lve cold electrodes disposed Vbetween said cathode'and plate, oneyof said coldelectrodes belngadapted to function as an oscillator anode, a

second offsaidi-cold electrodes being adaptedv to functionY as an oscillator gridand being disposed betweenvthe oscillator anode and the said plate, two of said cold Velectrodes being positively charged andv surroundingV the oscillator anode and oscillator grid, means'for applying said positive charge, the other of said cold electrodes being' adaptedto function-as av signalgrid andbeing disposed between said' oscillator grid and plate, said,

tube having associated therewith a'signalinput cathode, a tunableoscillator circuit connected to one of said oscillator electrodes', and anl automatic' volume control.` network electrically asso` Vcircuit connected between thesignal grid and the ,Y e

ciated with said signal grid for automatically-V varying the conversion` gainofV the tube# in re- Y sponse to variations in, thereceived 'signal'ampli- 6. A frequency converting-'device comprising the combination of av vacuum tube having a cathode, an oscillator anode, a grid llocated between said cathode and anode, meansfor applying a lpositive potential to said grid, ,afplateg an oscillator grid located between said Yoscillator anode and plate and arranged to have a negative oscillator grid and anode-,a circuit tuned' to: a local oscillation Y frequency coupled Vto said oscillator anode, said circuit being caused to oscillate by the vtransconductance with respect to said Voscillator anode, a signal control grid, a; capacitively re-1 active feedback circuit connected `between said feedback through said capacitively reactive Vcircuit, a circuit tnedjfto an incoming'signal. fre-y quency coupled to said signal control grid and an output circuit connected to said plate.

Y WALTER; VAN B. ROBERTS. u 

